The present invention relates to a radio terminal and fault detection method for detecting transmission power abnormalities.
The general electrical circuit for a known cellular telephone is shown in FIG. 10. When the baseband processor 1 outputs a transmission signal, that transmission signal is input to a variable gain amplifier 3 by way of a modulator 2. The variable gain amplifier 3 then performs power amplification according to the gain output from the transmission power controller 4 and outputs a power amplification signal. When the power amplification signal is input to a transmission power amplifier 5, the transmission power amplifier 5 amplifies the power of the power amplification signal and outputs this signal to an antenna 7 by way of a joint device 6. The antenna 7 thus transmits the power amplification signal to a base station utilizing the radio waves as a medium.
The gain of the variable gain amplifier 3 is set based on the downlink communication signal transmitted from the base station by the transmission power controller 4. In other words, this gain and the output power from the variable gain amplifier 3 are controlled by the base station. The transmission power output from the transmission power amplifier 5 is also controlled by the base station.
However, when a fault occurs in the variable gain amplifier 3, the transmission power controller 4, the transmission power amplifier 5, the joint device 6, or the antenna 7, the transmission power for transmission to the base station is a value unrelated to control by the base station. In other words, a transmission power fault will occur.
To detect these kinds of transmission power faults, a detector circuit 9 is added to the final stage of the transmission power amplifier 5 to monitor the transmission power output of the transmission power amplifier 5. The detector circuit 9 outputs the transmission power signal from the transmission power amplifier 5 to the baseband processor 1 by way of an A/D converter 9a. The A/D converter 9a output tolerance range (values) are stored in the baseband processor 1 to correspond one-to-one with the transmission power value settings as shown in FIG. 11. The baseband processor 1 can determine if a transmission power fault has occurred by determining whether the output from A/D converter 9a has deviated from the output tolerance range. Service personnel can, for example, detect a transmission power fault by using a cellular telephone without having to use dedicated test equipment.
When, for example, there is an extremely large differential between maximum transmission power and minimum transmission power, as in CDMA (Code Division Multiple Access) systems, a detector circuit 9 for monitoring transmission power, used as a circuit for detecting the above described transmission power faults, must be capable of detecting faults over an extremely wide range.